We have all seen the plethora of advertisements in the magazines about LED grow lights. When LEDs first hit the horticulture market they were little more than Light-Brite™ toys with expensive price tags and big promises. They claimed that each watt of LED lighting was equivalent to more than 10 watts of HID lighting, on top of which they asserted LEDs would produce no heat, have better penetration of light through the canopy, and that they would revolutionize the growing industry. Unfortunately, the early LEDs were unable to deliver on most of their promises.
LED stands for Light Emitting Diode. Unlike traditional light sources with delicate filaments, electrodes, or pressurized gas filled lamps (i.e. HIDs), LEDs are solid state electronics, and as such are more robust and longer lasting (Bourget, 2008). Solid state by its most simple definition means “made without any moving parts.” A flash memory card is solid state device, where as a typical hard drive is not. By not incorporating moving parts into the design, solid state electronics are less likely to break, wear out, or malfunction. This added level of reliability is one of the biggest benefits of LEDs. Current LEDs are rated for as many as 70,000 hours of operation before they reach the point where replacement is advisable. Although they will still be working at that point, at 70,000 hours of operation they will have reached a 30% diminishment in luminous output making it cost effective to replace them. Seventy-thousand hours means that a grower using LEDs will not change the diodes for almost 16 straight years, running 12 hours per day, every day.
LEDs have not always had the longevity and reliability they are able to deliver today. The history LEDs being used in horticultural applications started in the late 1980’s with crude arrays of red only (660 nanometer) LEDs. Early experimentation with LEDs in horticulture was driven by their potential for use in growing food for space travel. In the late 1990s the crops research group at the Kennedy Space Center conducted several studies on the yield and physiological response of several crops to LED lighting. LEDs became even more promising with two critical advances in LED technology; the advent of blue LEDs, and high output diodes. For a full timeline of LED lighting in horticulture please see the timeline below (HortScience Vol.43(7) Dec. 2008)
The advances in LED technology keep on coming; each decade LED prices have fallen by a factor of 10, while their performance has grown by a factor of 20 (a phenomenon known as Haitz’ Law). So it seems the future of LEDs is getting brighter! In the next blog we will look at the different applications of using LEDs for growing plants and see if they are close to delivering on their original promise of revolutionizing the horticultural world.